A friend commented that he
appreciated the surround sound descriptions and speaker layouts
outlined below. But he still did
not clearly understand surround sound. In other words, why multiple channels? Let's begin with the early attempts to use stereo audio in commercial
movie theaters. It
was successful if a viewer sat in a seat at
the stereo 'sweet spot' location or beyond. However, if
they sat closer, plus well left or right of the 'sweet spot', and viewed an actor screen center; they then heard the actor's voice emanating from the edge of the screen. Audiences found this
disconcerting.
Solution -- the sound of screen images now
radiate from their screen
location. Screen left images are directed to the left
speaker, screen right images to the right speaker, and center images to a center placed
speaker. Theater audio improvements continued with surround channels via rear placed speakers that allow for 'cool' effects. Star ships fly front to back, left to right,
diagonally,and circularly around the the room. A dedicated low frequency effects channel was also added that rocks theater audiences with exploding concussive sound. The latest Dolby Atmos/DTS-X commercial theater formats
now offer up to 64 'object oriented' channels that include above height
channels. Surround sound has come a long way since its early use in 1940.

Home
Theater Surround Sound FormatsThe balance of this page outlines the home
theatersurround
sound formats of Analog Dolby
Surround, Dolby Digital, and DTS. Chapter Six covers speaker and listener placement in more detail.

AnalogDolbySurround

Analog
Dolby
Surroundis
the original home audio surround sound format. Some
may recall vinyl LP quadraphonic audio. 'Quad' concealed additional
rear audio
channels within
a stereo recording. Analog Dolby Surround is a similar
format. The HiFi Beta VCR, the HiFi VHS VCR, and the Laser Disc were the
original home audio sources of Dolby Surround. Dolby surround sound was
available in two versions: Dolby
Surround and Dolby
Pro Logic.

Dolby
Surround routes stereoaudio
to a circuit
that takes thedifference
between the left and right stereochannels.
This matrix difference is amonaural
and frequency limited (almost
no bass) channelrouted to left and right rear placed speakers.

Dolby
Pro Logic
is also matrix derived from a stereo recording. But Pro Logic adds a center channel, a
low pass filtered sub woofer channel, and modifies the
left
and right channels to set the left/right 'audio edges' of the image.
The rear channel is produced as Dolby Surround. The
following outlines the matrix logic that created all five channels from
two channels of audio via a digital sound processing integrated chip: - Rear = (left channel - right channel)
- Center =
[(left channel + right channel) - (rear channel)] - Left edge = (left channel - center channel) - Right edge = (right channel - center channel) - Sub woofer = low pass filtered (left channel + right channel)

Digital Dolby & DTS Surround Sound

Digital surround (for the most part) eliminates 'difference' matrix
processing.Each channel
is recorded as a discrete channel routed
to a dedicated
speaker.The DVD and Blu-ray disc employ the Dolby and DTS formats. Broadcast
satellite, cable, and off-air TV use Dolby formats. Dolby Digital and DTS are produced in
the following versions.

Dolby HD
and
DTS
HD Master Audio arelosslessdigital
processing formats that offer almost bit for bit
recreations of the original studio master recording. The
concept of
lossless recording is addressed in Chapter Three. The
important
point: lossless processing is a significant step forward in
fidelity.
Dolby
Digital Plusand
DTS HD are lossy
digital formats. Lossy formats are a step down from
the lossless process. But they offer improved
performance over
standard Dolby Digital and DTS. Lossy is covered in Chapter
Three. 2014 Dolby Atmos
adds
two to four overhead "height
channels"
to the home theater 5.1, 6.1, and 7.1 layouts. Atmos is referred to as
an "object oriented" effect. Digital 'Tags' are assigned to
objects
in the sound mix and directed to a specific speaker.

Dolby Atmos also offers an optional version with 32 channels. It consists
of
24 speakers on
the floor paired with 10 overhead speakers.
2015DTS:X
- DTS
joined the object
oriented with above channel surround sound party.